Suzuki-Miyaura Cross-Coupling Reaction Using Palladium Catalysts Supported on Phosphine Periodic Mesoporous Organosilica.

Phosphine periodic mesoporous organosilicas (R-P-PMO-TMS: R=Ph, tBu), which possess electron-donating alkyl substituents on the phosphorus atom, were synthesized using bifunctional compounds with alkoxysilyl- and phosphino groups, bis[3-(triethoxysilyl)propyl]phenylphosphine borane (1 a) and bis[3-(triethoxysilyl)propyl]-tert-butylphosphine borane (1 b). Immobilization of Pd(0) species was performed to give R-P-Pd-PMO-TMS: R=Ph (2 a), tBu (3 a), respectively. The Pd(0) immobilized 2 a and 3 a were applicable as catalysts for Suzuki-Miyaura cross-coupling reactions of aryl chlorides with phenylboronic acid. It was revealed that 3 a bearing more electron-donating tBu groups exhibited higher catalytic activity. Various functional groups including both electron withdrawing and donating substituents were compatible in the system. The recyclability of 3 a was examined to support its moderate utility for the recycle use.

1,10-Phenanthroline-based periodic mesoporous organosilica: from its synthesis to its application in the cobalt-catalyzed alkyne hydrosilylation.

1,10-Phenanthroline (Phen) is a typical ligand for metal complexation and various metal/Phen complexes have been applied as a catalyst in several organic transformations. This study reports the synthesis of a Phen-based periodic mesoporous organosilica (Phen-PMO) with the Phen moieties being directly incorporated into the organosilica framework. The Phen-PMO precursor, 3,8-bis[(triisopropoxysilyl)methyl]-1,10-phenanthroline (1a), was prepared via the Kumada-Tamao-Corriu cross-coupling of 3,8-dibromo-1,10-phenanthroline and [(triisopropoxysilyl)methyl]magnesium chloride. The co-condensation of 1a and 1,2-bis(triethoxysilyl)ethane in the presence of P123 as the template surfactant afforded Phen-PMO 3 with an ordered 2-D hexagonal mesoporous structure as confirmed by nitrogen adsorption/desorption measurements, X-ray diffraction, and transition electron microscopy. Co(OAc)2 was immobilized on Phen-PMO 3, and the obtained complex showed good catalytic activity for the hydrosilylation reaction of phenylacetylene with phenylsilane.

Virus Inactivation Based on Optimal Surfactant Reservoir of Mesoporous Silica.

SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) caused a pandemic in 2019 and reaffirmed the importance of environmental sanitation. To prevent the spread of viral infections, we propose the application of a mesoporous silica (MS)-based virus-inactivating material. MS is typically synthesized using a micellar surfactant template; hence, the intermediate before removal of the surfactant template is expected to have a virus-inactivating activity. MS-CTAC particles filled with cetyltrimethylammonium chloride (CTAC), a cationic surfactant with an alkyl chain length of 16, were used to test this hypothesis. Plaque assays revealed that the MS-CTAC particles inactivated the enveloped bacteriophage φ6 by approximately 4 orders of magnitude after a contact time of 10 min. The particles also indicated a similar inactivation effect on the nonenveloped bacteriophage Qß. In aqueous solution, CTAC loaded on MS-CTAC was released until the equilibrium concentration of loading and release on MS was reached. The released CTAC acted on viruses. Thus, MS is likely a good reservoir for the micellar surfactant. Surfactant readsorption also occurred in the MS particles, and the highest retention rate was observed when micellar surfactants with alkyl chain lengths appropriate for the pore size were used. The paper containing MS-CTAC particles was shown to maintain stable viral inactivation for at least three months in a typical indoor environment. Applying this concept to indoor wallpaper and air-conditioning filters could contribute to the inactivation of viruses in aerosols. These findings open possibilities for mesoporous materials with high surface areas, which can further develop into virus inactivation materials.

Nanoporous Substrates with Molecular-Level Perfluoroalkyl/Alkylamide Surface for Laser Desorption/Ionization Mass Spectrometry of Small Proteins.

The rapid detection of biomolecules greatly contributes to health management, clinical diagnosis, and prevention of diseases. Mass spectrometry (MS) is effective for detecting and analyzing various molecules at high throughput. However, there are problems with the MS analysis of biological samples, including complicated separation operations and essential pretreatments. In this study, a nanostructured organosilica substrate for laser desorption/ionization mass spectrometry (LDI-MS) is designed and synthesized to detect peptides and small proteins efficiently and rapidly. The surface functionality of the substrate is tuned by perfluoroalkyl/alkylamide groups mixed at a molecular level. This contributes to both lowering the surface free energy and introducing weak anchoring sites for peptides and proteins. Analyte molecules applied onto the substrate are homogeneously distributed and readily desorbed by the laser irradiation. The organosilica substrate enables the efficient LDI of various compounds, including peptides, small proteins, phospholipids, and drugs. An amyloid ß protein fragment, which is known as a biomarker for Alzheimer's disease, is detectable at 0.05 fmol µL-1. The detection of the amyloid ß at 0.2 fmol µL-1 is also confirmed in the presence of blood components. Nanostructured organosilica substrates incorporating a molecular-level surface design have the potential to enable easy detection of a wide range of biomolecules.

Hydrogen Production from Methanol-Water Mixture over Immobilized Iridium Complex Catalysts in Vapor-Phase Flow Reaction.

Invited for this month's cover is the group of Shinji Inagaki from Toyota Central R&D Laboratories Inc. and Ken-ichi Fujita from Kyoto University. The image shows iridium complexes immobilized on the channel walls of periodic mesoporous organosilica, which catalyze the dehydrogenation of a methanol-water mixture to produce hydrogen and carbon dioxide. The Full Paper itself is available at 10.1002/cssc.202002557.

Hydrogen Production from Methanol-Water Mixture over Immobilized Iridium Complex Catalysts in Vapor-Phase Flow Reaction.

CO-free hydrogen production from methanol and water by using transition metal complex catalysts has attracted increasing attention. However, liquid-phase batch reactions using homogeneous catalysts are impractical for large-scale operations, owing to the consumption of bases and the use of organic solvents or additives. This study concerns a novel method for continuous hydrogen production from a simple methanol-water solution under vapor-phase flow. The reaction is catalyzed by an anionic iridium bipyridonate (Ir-bpyd) complex immobilized on a periodic mesoporous organosilica. The liquid-phase batch reaction using homogeneous anionic Ir-bpyd complex is immediately deactivated, owing to CO2 generation, whereas no catalyst deactivation is observed in the vapor-phase flow reaction because CO2 is smoothly removed from the catalyst bed, enabling continuous hydrogen production without the addition of a base. Thus, the critical problems pertaining to homogeneous catalysts are overcome.

Direct nanoimprinting of nanoporous organosilica films consisting of covalently crosslinked photofunctional frameworks.

Nanoimprinting methods have been used widely to prepare various patterned or nanostructured thin films from inorganic or organic components. However, the accumulation of large functional aromatic groups in covalently crosslinked nanoimprints is challenging, due to the difficulty in controlling the fluidity and reactivity of the precursor films. In this work, nanoimprinting of naphthalimide-silica sol-gel films results in vertically oriented nanoporous structures consisting of covalently crosslinked UV-absorbing frameworks. The nanoimprinted films demonstrate potential as robust analytical substrates for laser desorption/ionization mass spectrometry (LDI-MS). The sol-gel polycondensation behavior of the precursors is examined using 29Si NMR spectroscopy to determine reaction conditions suitable for nanoimprinting. The inorganic-organic hybrid frameworks containing a high density of naphthalimide groups exhibit small volume shrinkage during the polycondensation reactions, which leads to desired nanoimprinting. Various bio-related compounds on the order of picomole to femtomole quantities are detectable by LDI-MS measurements using the nanoimprinted substrates. To improve their user-friendliness and signal intensity in LDI-MS analysis, the nanoimprinted substrates are patterned with surface-modified silica nanoparticles. The direct formation of surface nanostructures by nanoimprinting of functional organosilica films may open a new path to developing optically and electronically functional materials, thereby widening their utility.

Lanthanide-Grafted Bipyridine Periodic Mesoporous Organosilicas (BPy-PMOs) for Physiological Range and Wide Temperature Range Luminescence Thermometry.

2,2'-Bipyridine is the most widely used chelating ligand for developing metal complexes in coordination and supramolecular chemistry. Here, we present a series of three bipyridine periodic mesoporous organosilicas (BPy-PMOs) grafted with lanthanide ß-diketonate complex for the purpose of obtaining thermochromic materials, which can be employed as ratiometric temperature sensors. Such thermometers are based on the ratio of two emission intensity peaks and are not affected by factors such as alignment or optoelectronic drift of the excitation source and detectors. Three thermometric systems are studied: Dy-Dy, Tb-Sm, and Tb-Eu with the first two showing very attractive performance. For the first two systems, some of the best reported to date relative sensitivities are observed. In the BPy-PMO@Dy(acac)3 system, it is very unusual that the 4I15/2→ 6H15/2 transition is already occupied at low temperature such as 200 K, which influences its thermometric behavior. The Tb-Sm shows excellent performance in the physiological range and when suspended in water. We have additionally confirmed that the BPy-PMO hybrid materials lack toxicity to human cells, proving them very promising candidates for biomedical thermometric applications.

Ab initio study on the excited states of pyrene and its derivatives using multi-reference perturbation theory methods.

Low-lying singlet excited states of pyrene derivatives originated from the 1La and 1Lb states of pyrene have decisive influences on their absorption and fluorescence emission behaviors. Calculation of these excited states with quantitative accuracy is required for the theoretical design of pyrene derivatives tailored to target applications; this has been a long-standing challenge for ab initio quantum chemical calculations. In this study, we explore an adequate computational scheme through calculations of pyrene and its phenyl-substituted derivatives using multi-reference perturbation theory (MRPT) methods. All valence π orbitals on the pyrene moiety were assigned to the active orbitals. Computational load was reduced by restricting the electron excitations within the active orbitals in the preparation of reference configuration space. A generalized multi-configuration quasi-degenerate perturbation theory (GMCQDPT) was adopted to treat the reference space other than the complete active space. The calculated 1La and 1Lb excitation energies of pyrene are in good agreement with the experimental values. Calculations of 1,3,6,8-tetraphenyl pyrene suggest that the energetic ordering of 1La and 1Lb is inverted through tetraphenyl substitution and its lowest singlet excited state is the 1La parentage of pyrene, which is consistent with the experimentally deduced scheme. These results are not readily obtained by MRPT calculations with a limited number of active orbitals and single-reference theory calculations. Diphenyl pyrenes (DPPy) were also calculated at the same level of theory to investigate the dependence on the substitution positions of phenyl groups.

Heterogeneous water oxidation photocatalysis based on periodic mesoporous organosilica immobilizing a tris(2,2'-bipyridine)ruthenium sensitizer.

A periodic mesoporous organosilica (PMO) containing 2,2'-bipyridine groups (BPy-PMO) has been shown to possess a unique pore wall structure in which the 2,2'-bipyridine groups are densely and regularly packed. The surface 2,2'-bipyridine groups can function as chelating ligands for the formation of metal complexes, thus generating molecularly-defined catalytic sites that are exposed on the surface of the material. We here report the construction of a heterogeneous water oxidation photocatalyst by immobilizing several types of tris(2,2'-bipyridine)ruthenium complexes on BPy-PMO where they function as photosensitizers in conjunction with iridium oxide as a catalyst. The Ru complexes produced on BPy-PMO in this work were composed of three bipyridine ligands, including the BPy in the PMO framework and two X2bpy, denoted herein as Ru(X)-BPy-PMO where X is H (2,2'-bipyridine), Me (4,4'-dimethyl-2,2'-bipyridine), t-Bu(4,4'-di-tert-butyl-2,2'-bipyridine) or CO2Me (4,4'-dimethoxycarbonyl-2,2'-bipyridine). Efficient photocatalytic water oxidation was achieved by tuning the photochemical properties of the Ru complexes on the BPy-PMO through the incorporation of electron-donating or electron-withdrawing functionalities. The reaction turnover number based on the amount of the Ru complex was improved to 20, which is higher than values previously obtained from PMO systems acting as water oxidation photocatalysts.

Fast and stable vapochromic response induced through nanocrystal formation of a luminescent platinum(II) complex on periodic mesoporous organosilica.

A hybrid vapoluminescent system exhibiting fast and repeatable response was constructed using periodic mesoporous organosilica with bipyridine moieties (BPy-PMO) and a Pt(II) complex bearing a potentially luminescent 2-phenylpyridinato (ppy) ligand. An intense red luminescence appeared when the Pt(II)-complex immobilised BPy-PMO was exposed to methanol vapour and disappeared on exposure to pyridine vapour. The ON-OFF vapochromic behaviour occurred repeatedly in a methanol/pyridine/heating cycle. Interestingly, a rapid response was achieved in the second cycle and cycles thereafter. Scanning and transmission electron microscopies (SEM/TEM), absorption and emission, and nuclear magnetic resonance spectroscopies, mass spectrometry, and powder X-ray diffraction indicated that methanol vapour induced Si-C cleavage and thus liberated [Pt(ppy)(bpy)]Cl (bpy = 2,2'-bipyridine) from the BPy-PMO framework. Furthermore, the self-assembling properties of the Pt(II) complex resulted in the formation of highly luminescent micro/nanocrystals that were homogeneously dispersed on the porous support. The unique vapoluminescence triggered by the unprecedented protodesilylation on exposure to protic solvent vapour at room temperature is attributable to BPy-PMO being a giant ligand and an effective vapour condenser. Consequently, this hybrid system presents a new strategy for developing sensors using bulk powdery materials.

Cooperative Catalysis of an Alcohol Dehydrogenase and Rhodium-Modified Periodic Mesoporous Organosilica.

The combined use of a metal-complex catalyst and an enzyme is attractive, but typically results in mutual inactivation. A rhodium (Rh) complex immobilized in a bipyridine-based periodic mesoporous organosilica (BPy-PMO) shows high catalytic activity during transfer hydrogenation, even in the presence of bovine serum albumin (BSA), while a homogeneous Rh complex exhibits reduced activity due to direct interaction with BSA. The use of a smaller protein or an amino acid revealed a clear size-sieving effect of the BPy-PMO that protected the Rh catalyst from direct interactions. A combination of Rh-immobilized BPy-PMO and an enzyme (horse liver alcohol dehydrogenase; HLADH) promoted sequential reactions involving the transfer hydrogenation of NAD+ to give NADH followed by the asymmetric hydrogenation of 4-phenyl-2-butanone with high enantioselectivity. The use of BPy-PMO as a support for metal complexes could be applied to other systems consisting of a metal-complex catalyst and an enzyme.

Heterogeneous hydrosilylation reaction catalysed by platinum complexes immobilized on bipyridine-periodic mesoporous organosilicas.

The utility of a bipyridine periodic mesoporous organosilica, BPy-PMO, as a support material of a hydrosilylation catalyst was investigated in the hydrosilylation of phenylacetylene with trimethoxysilane. [PtMe2(BPy-PMO)] (1) exhibited a moderate catalytic activity, whereas the reaction was successfully catalysed by [PtMe2(BPy-PMO-TMS)] (2) bearing end-capped TMS groups on the surface. Spectroscopic analyses of 2 revealed that the porous structure of BPy-PMO-TMS remained almost unchanged through the reaction. The hot filtration test supported the nonleaching property of 2, thereby exhibiting good reusability without the loss of the product yields.

Synthesis and Optical Applications of Periodic Mesoporous Organosilicas.

Periodic mesoporous organosilicas (PMOs), synthesized via surfactant-directed self-assembly of a polysilylated organic precursor (R[Si(OR')3]n; n≥2, R: organic group), are promising candidates such as catalysts and adsorbents, and for use in optical and electrical devices, owing to their high surface area, well-defined nanoporous structure, and highly functional organosilica framework. Their framework functionality can be widely tuned by selecting appropriate organic groups and controlling their arrangement. This chapter describes the synthesis and structure of PMOs with simple organic groups such as ethane and benzene, and the unique properties and optical applications of functional PMOs. Special light-harvesting properties and their exploitation in photocatalysis, highly emissive PMOs and their application to color-tunable transparent films, hole-transporting PMOs and their use in organic solar cells, and PMOs containing chelating ligands and their use as solid supports for heterogeneous metal complex catalysis are described.

Charge Separation in a Multifunctionalized Framework of Hydrogen-Bonded Periodic Mesoporous Organosilica.

Integration of functional molecular parts into nanoporous materials in a state that allows intermolecular charge or energy transfer is one of the key approaches to the development of photofunctional and electroactive materials. Herein, we report charge separation in a functionalized framework of a periodic mesoporous organosilica (PMO) self-assembled by hydrogen bonds. Electroactive π-conjugated organic species with different electron-donating and electron-accepting properties were selectively fixed onto the external surface of a nanoparticulate PMO, within the pore wall, and onto the surface of the internal mesopore. UV irradiation of the modified PMO resulted in photoinduced electron transfer and charge separation from the external surface to the pore wall and from the pore wall to the surface of the internal mesopores. These results suggest the high potential of multifunctionalized PMOs in the construction of photocatalytic reaction fields.

Re(bpy)(CO)3 Cl Immobilized on Bipyridine-Periodic Mesoporous Organosilica for Photocatalytic CO2 Reduction.

This paper describes the physicochemical properties of a rhenium (Re) complex [Re(bpy)(CO)3 Cl] immobilized on a bipyridine-periodic mesoporous organosilica (BPy-PMO) acting as a solid support. The immobilized Re complex generated a metal-to-ligand charge transfer absorption band at 400 nm. This wavelength is longer than that exhibited by Re(bpy)(CO)3 Cl in the polar solvent acetonitrile (371 nm) and is almost equal to that in nonpolar toluene (403 nm). The photocatalytic activity of this heterogeneous Re complex was lower than that of a homogeneous Re complex due to the reduced phosphorescence lifetime resulting from immobilization. However, the catalytic activity was enhanced by the co-immobilization of the ruthenium (Ru) photosensitizer [Ru(bpy)3 ]2+ on the PMO pore surfaces. Quantum chemical calculations suggest that electron transfer between the Ru and Re complexes occurs through interactions between the molecular orbitals in the pore walls. These results should have applications to the design of efficient heterogeneous CO2 reduction photocatalysis systems.

Enhanced durability of an iridium-bipyridine complex embedded into organosilica nanotubes for water oxidation.

Heterogeneous metal complex catalysts for the water oxidation reaction have ever been desired for the development of devices simulating photosynthesis. This paper describes the design of highly active and robust heterogeneous iridium complex catalysts for chemical water oxidation. The heterogeneous catalyst (Ir-BPy-NT) was prepared by the post-synthetic metalation of bipyridine-containing mesoporous organosilica nanotubes (BPy-NT) with an [IrCp*Cl(µ-Cl)]2 (Cp* = η5-pentamethylcyclopentadienyl) complex. The as-prepared Ir-BPy-NT catalyst showed enhanced durability with high reaction activity compared to the analogous homogeneous and the conventional heterogeneous ones, due to the stable nanotube structures as well as the isolated active sites. The unique one-dimensional nanotubes with large pore diameters can also reduce the diffusion limitation and facilitate the transport of reactants and products during reactions.

Photocatalytic CO2 Reduction by Periodic Mesoporous Organosilica (PMO) Containing Two Different Ruthenium Complexes as Photosensitizing and Catalytic Sites.

A periodic mesoporous organosilica (PMO) containing 2,2'-bipyridine (bpy) ligands within the framework (BPy-PMO) has great potential for designing novel catalysts by modifying metal complexes. A photosensitizing site (Ru(PS)) was introduced by treating cis-[Ru(bpy)2 (dimethylsulfoxide)Cl]Cl with BPy-PMO. Then a catalytic site (Ru(Cat)) was brought in Ru(PS)x -BPy-PMO by reaction with a ruthenium polymer [Ru(CO)2 Cl2 ]n . The stepwise modification of BPy-PMO successfully affords a novel photocatalyst Ru(PS)x -Ru(Cat)y -BPy-PMO. The molar fractions (x, y) of Ru(PS) and Ru(Cat) were determined by energy dispersive X-ray (EDX) measurement and quantification of the amount of CO emitted in the photo-decarbonylation of Ru(Cat), respectively. Photochemical CO2 reduction (λex >430 nm) by Ru(PS)x -Ru(Cat)y -BPy-PMO in a CO2 -saturated N,N-dimethylacetamide/water solution containing 1-benzyl-1,4-dihydronicotinamide catalytically produced CO and formate. The total turnover frequency of CO and formate reached more than 162 h-1 on x=0.11 and y=0.0055. The product selectivity (CO/formate) became large when the ratio of Ru(PS)-to-Ru(Cat) (x/y) was increased. The photocatalysts can be recycled at least three times without losing their catalytic activity, demonstrating that the Ru(PS) and Ru(Cat) units were strongly immobilized on the BPy-PMO framework.

Heterogeneous Molecular Systems for Photocatalytic CO2 Reduction with Water Oxidation.

Artificial photosynthesis-reduction of CO2 into chemicals and fuels with water oxidation in the presence of sunlight as the energy source-mimics natural photosynthesis in green plants, and is considered to have a significant part to play in future energy supply and protection of our environment. The high quantum efficiency and easy manipulation of heterogeneous molecular photosystems based on metal complexes enables them to act as promising platforms to achieve efficient conversion of solar energy. This Review describes recent developments in the heterogenization of such photocatalysts. The latest state-of-the-art approaches to overcome the drawbacks of low durability and inconvenient practical application in homogeneous molecular systems are presented. The coupling of photocatalytic CO2 reduction with water oxidation through molecular devices to mimic natural photosynthesis is also discussed.

Heterogeneous Catalysis for Water Oxidation by an Iridium Complex Immobilized on Bipyridine-Periodic Mesoporous Organosilica.

Heterogenization of metal-complex catalysts for water oxidation without loss of their catalytic activity is important for the development of devices simulating photosynthesis. In this study, efficient heterogeneous iridium complexes for water oxidation were prepared using bipyridine-bridged periodic mesoporous organosilica (BPy-PMO) as a solid chelating ligand. The BPy-PMO-based iridium catalysts (Ir-BPy-PMO) were prepared by postsynthetic metalation of BPy-PMO and characterized through physicochemical analyses. The Ir-BPy-PMOs showed high catalytic activity for water oxidation. The turnover frequency (TOF) values for Ir-BPy-PMOs were one order of magnitude higher than those of conventional heterogeneous iridium catalysts. The reusability and stability of Ir-BPy-PMO were also examined, and detailed characterization was conducted using powder X-ray diffraction, nitrogen adsorption, (13) C DD MAS NMR spectroscopy, TEM, and XAFS methods.